A storage apparatus includes a cache memory for temporarily storing data. In response to a write access from a host computer to a disk drive, the storage apparatus writes write data to the cache memory, upon which it notifies the host computer of the completion of write processing; and in response to a read access from the host computer to the disk drive, the storage apparatus reads data from the cache memory on condition that the read data has a cache hit. As a result, high-speed access is realized.
However, since the cache memory is often composed of a volatile memory, if power supply from a power source to the cache memory stops due to, for example, a power failure, data in the cache memory sometimes may sometimes be loss. Therefore, a large-capacity battery is mounted in the storage apparatus, so that if the power supply from the power source to the cache memory stops due to, for example a power failure, the large-capacity battery supplies the electric power to the cache memory, thereby preventing destruction of data in the cache memory even in the case of a power failure and allowing business activities to continue based on the data in the cache memory.
However, if the large-capacity battery is mounted in the storage apparatus, the cost of the storage apparatus increases by a cost amount of the mounted large-capacity battery. Also, even if the large-capacity battery is used, the capacity of the battery is limited. So, if the power interruption duration due to the power failure increases, there may be no other choice but the data in the cache memory may be destroyed and the business activities may have to be stopped.
On the other hand, if a small-capacity, small-sized battery that can be charged from the power source is mounted in the storage apparatus, it is possible to curb an increase in the cost as opposed to the case of mounting the large-capacity battery. In this case, it is possible to adopt a method of: saving data and information, which are stored in the volatile memory, to the nonvolatile memory at the time of power interruption caused by the occurrence of a power failure; and, at the time of power recovery when the power failure is solved, supplying the electric power from the small battery to the volatile memory, returning the data and information, which are stored in the nonvolatile memory, to the volatile memory, and resuming the business activities based on the data and information returned to the volatile memory.
When activating the storage apparatus under the circumstances described above as disclosed in Patent Literature 1, it is possible to adopt a method of selecting and activating two or more activation control units, whose power consumption of the entire load as recognized by the power source is equal to or less than specified electric power that is less than the maximum electric power that can be supplied by the power source, from among a plurality of activation control units.